The diurnal cycle of rainfall and its regional variation over Sumatera Island, Indonesian Maritime Continent, are examined using Tropical Rainfall Measuring Mission (TRMM) satellite precipitation radar (PR) and intensive rawinsonde sounding data. The TRMM PR sensor can detect raindrops directly, regardless of ground and cloud conditions, and can distinguish between convective and stratiform types of rainfall. Rainfall variation over this area was found to have the following characteristics: 1) convective rainfall with a broad peak between 1500 and 2000 LT predominates over the land region of Sumatera Island, whereas rainfall in the early morning, composed almost equally of stratiform and convective types, is predominant over the surrounding sea region. 2) A rainfall peak in the daytime and one in the nighttime migrate with time starting from the southwestern coastline of the island into the inland and offshore regions, respectively. The distance of each rainfall peak migration from the coastline ... Abstract The diurnal cycle of rainfall and its regional variation over Sumatera Island, Indonesian Maritime Continent, are examined using Tropical Rainfall Measuring Mission (TRMM) satellite precipitation radar (PR) and intensive rawinsonde sounding data. The TRMM PR sensor can detect raindrops directly, regardless of ground and cloud conditions, and can distinguish between convective and stratiform types of rainfall. Rainfall variation over this area was found to have the following characteristics: 1) convective rainfall with a broad peak between 1500 and 2000 LT predominates over the land region of Sumatera Island, whereas rainfall in the early morning, composed almost equally of stratiform and convective types, is predominant over the surrounding sea region. 2) A rainfall peak in the daytime and one in the nighttime migrate with time starting from the southwestern coastline of the island into the inland and offshore regions, respectively. The distance of each rainfall peak migration from the coastline ...

Accurate precipitation observations are crucial for water resources management and as inputs for a gamut of hydrometeorological applications. Precipitation data from Integrated Multi-Satellite Retrievals for Global Precipitation Measurement (GPM) (IMERG) have recently been widely used to complement traditional rain gauge systems. However, the satellite precipitation data needs to be validated before being widely used in the applications and this is still missing over the Indonesian maritime continent (IMC). We conducted a validation of the IMERG product version 6 for this region. The evaluation was carried out using gauge data in the period from 2016 to 2020 for three types of IMERG: Early (E), Late (L), and Final (F) from annual, monthly, daily and hourly data. In general, the annual and monthly data from IMERG showed a good correlation with the rain gauge, with the mean correlation coefficient (CC) approximately 0.54–0.78 and 0.62–0.79, respectively. About 80% of stations in the IMC area showed a very good correlation between gauge data and IMERG-F estimates (CC = 0.7–0.9). For the daily assessment, the CC value was in the range of 0.39 to 0.44 and about 40% of stations had a correlation of 0.5–0.7. IMERG had a fairly good ability to detect daily rain in which the average probability of detection (POD) for all stations was above 0.8. However, the false alarm ratio (FAR) value is quite high (<0.5). For hourly data, IMERG’s performance was still poor with CC around 0.03–0.28. For all assessments, IMERG generally overestimated rainfall in comparison with rain gauge. The accuracy of the three types of IMERG in IMC was also influenced by season and topography. The highest and lowest CC values were observed for June–July–August and December–January–February, respectively. However, categorical statistics (POD, FAR and critical success index) did not show any clear seasonal variation. The CC value decreased with higher altitude, but with slight difference for each IMERG type. For all assessments conducted, IMERG-F generally showed the best rainfall observations in IMC, but with slightly difference from IMERG-E and IMERG-L. Thus, IMERG-E and IMERG-L data that had a faster latency than IMERG-F show potential to be used in rainfall observations in IMC.

Vertical wind disturbances are frequently observed during midsummer afternoons in association with cumulus convection. To examine the relation of these wind disturbances to atmospheric stability and turbulence intensity, we carried out intensive observations of wind, temperature and humidity over a large vertical region extending from the boundary layer to the lower stratosphere using UHF/VHF radars and radiosondes at Shiga, Japan (35°N, 136°E). The wind disturbances propagate quickly into the upper troposphere just after 1500 local standard time (LST) when the level of free convection (LFC) descends below the top of the mixed layer, while before that, the disturbances are confined in the mixed layer. However, strong turbulence is largely confined to the region below 3 km even after 1500 LST, suggesting that the height of 3 km corresponds to the top of cumuli, while the wind disturbances above are due to gravity waves generated in association with cumulus convection. In addition, stratospheric disturbances were examined for 12 cases of midsummer disturbances using routine observational data taken with a VHF radar in a height region of 5–24 km. Wind disturbances are observed in the lower stratosphere when turbulence as well as wind disturbances are strong in the whole troposphere. The stratospheric disturbances are dominant in two regions below and above a height of 18 km where the background horizontal wind is weak. Long‐period disturbances are observed only in the lower region. This fact suggests that the height of 18 km is a critical level for the long‐period gravity waves. The existence of a strong turbulent layer around 18 km is consistent with this inference.

Characteristics of sea-breeze circulation over the tropical site of Jakarta, Indonesia, have been documented based on analyses of satellite images and data from long-term L-band boundary layer radar measurements carried out at Serpong (6.4°S, 106.7°E). Inspection of satellite imagery reveals that a sea-breeze front develops well along the northern coastal plain of West Java and propagates inland until its structure is deformed over complex topography. It is found that the sea-breeze signal detected by the boundary layer radar is most well defined during the dry season months of July–October. In all of these months, radar observations indicate a late afternoon intensification of sea-breeze flow in the 0.5–0.8-km height range between 1700 and 1800 LT, which is not elucidated upon by surface measurements. The effect of weather conditions on the sea-breeze pattern is investigated by using a cloudiness index derived from data of incoming solar radiation. The results show that sea-breeze intrusion over... Abstract Characteristics of sea-breeze circulation over the tropical site of Jakarta, Indonesia, have been documented based on analyses of satellite images and data from long-term L-band boundary layer radar measurements carried out at Serpong (6.4°S, 106.7°E). Inspection of satellite imagery reveals that a sea-breeze front develops well along the northern coastal plain of West Java and propagates inland until its structure is deformed over complex topography. It is found that the sea-breeze signal detected by the boundary layer radar is most well defined during the dry season months of July–October. In all of these months, radar observations indicate a late afternoon intensification of sea-breeze flow in the 0.5–0.8-km height range between 1700 and 1800 LT, which is not elucidated upon by surface measurements. The effect of weather conditions on the sea-breeze pattern is investigated by using a cloudiness index derived from data of incoming solar radiation. The results show that sea-breeze intrusion over...